A year ago I bought a pair of Doop skates (https://doopshop.com/). Skates that attach to normal shoes. Sometimes it is nice if you don't have carry a pair of shoes, but can just take off your skates.

You can buy them different types of frames and I got them with a 3x110 setup. Big wheels roll better and normally I am on 4x110. And I didn't yet have a 3x110 frame.

Unfortunately, from the start they were very unstable on rough surface. They are perfectly fine on smooth tarmac. But horrible on rough tarmac or brick roads.

I assumed that the concept was just a bad idea and planned to mount the frames on normal speed skating boots. Last Friday put them on my old Fila F100 boots and went to the Amsterdam Friday Night skate. It was a disaster. I could easily keep up on smooth tarmac, but I could barely skate on brick roads, etc. Way worse even then when I used them in the original doop skate configuration.

I have used a Cado Motus 4x110 frame on those Fila boots for years. So I was really surprised that 3x110 would be so extremely unstable.

Looking at the frames I assumed the difference was due to deck height. But when I measured both frames, the Cado Motus frame measures 105 mm at the front and 115 mm at the rear (give or take a mm, I can't measure that accurately). The doop frame measures 110mm at the front and 120mm at the rear.

So the difference is roughtly 5mm. It that really what is causing the instability or is something else going on?

3-wheel frames may be short (FSK/speed slalom/etc) and long (speed skating). Your frame is < 10 inch long and has length equal to 4x80mm frame. So it's maneuverable

Does length make such a big difference? Both 4x110 and 4x90 are perfectly fine. Of course, the 4x110 is way better on rough surface, but 4x90 is quite usable as well. The 3x110 is indeed shorter than my 4x90, but would that make such a huge difference?

a large part of the smoothness or roughness depends on how many simultaneous points of contact with pavement surface you can have at any one instant of time. The more points the smoother the feel. Think of just one wheel... it has to follow each and every rise and dip. Two wheels are about the same as the front wheel rises and falls with every contour and so does the rear wheel. When you get to three wheels some smoothing happens because it is highly unlikely that all three wheels will encounter the same rise/fall at the same instant. When you have 4 or 5 wheels they can never go down into the deepest dips and so the ride is smoother and the front/back rocking motion that you'd have on a 2 wheel setup is minimized.

edit: wheel size also plays a significant role in smoothness. A small wheel can fall deeply into dips when a very large wheel will simply bridge over the dip.

So... long frame is not "directly" related to smooth but seems to be because more wheels and bigger wheels drive a longer frame.

or maybe not! I'm open to rebuttal discussion!

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Last edited by bjvircks; June 26th, 2017 at 11:02 PM.
Reason: expanding on a couple of points.

What sort of shoe are you wearing? If it has a soft sole that could allow the doop part of your setup to wobble no matter how rigidly you hold your foot. And if the wheels are wobbling enough to get further on their edges while you are trying to skate a straight line, I could see that causing problems.

Sketchers has a few lines of shoes that have thin soles. Or you could go the Vibram Five Finger shoes route. Maybe a good first step would be dress up shoes, which tend to have less cushioning than cross trainers.

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I have never liked 3 wheels setups of any kind on rough surfaces including 3x125. I use a 5x80 frame for my 3x125 setup. On a rough surface, I would much rather have the 5x80 instead of the 3x125. Just like bjvircks, fewer wheels equals rougher ride and a bigger chance for the wheels to take wicked detours on the edges of bricks or cracks in the road. Think of it this way, 3 wheels setups are essentially teeter totters that pivot about the middle wheel. If your skates are only touching the ground on the middle wheel while going over a bump, then it doesn't take much force to make your skate spin around by pivoting about that 2nd wheel.

What sort of shoe are you wearing? If it has a soft sole that could allow the doop part of your setup to wobble no matter how rigidly you hold your foot. And if the wheels are wobbling enough to get further on their edges while you are trying to skate a straight line, I could see that causing problems.

Note this is is not so much about Doop skates as a whole, I know that shoes make a big difference, but about mounting the 3x110 frames on a Fila F100 boot. Fila F100 boots are stiff, low speed skating boots. Unfortunately, they are not thermoplastic. They are not ideal, but work well enough with the other frames I have (4x90, 4x100, 4x110).

Quote:

Originally Posted by Stroopwafel

Maybe also the type of 110mm wheels you used?

I used the wheels that came with the Doop skates. Not great wheels, but they roll well enough.

Quote:

Originally Posted by kufman

I have never liked 3 wheels setups of any kind on rough surfaces including 3x125. I use a 5x80 frame for my 3x125 setup. On a rough surface, I would much rather have the 5x80 instead of the 3x125. Just like bjvircks, fewer wheels equals rougher ride and a bigger chance for the wheels to take wicked detours on the edges of bricks or cracks in the road.

One experiment I can try is to put 3 wheels per frame in my 4x110 frames and then compare that to the same wheels in the 3x110.

I used the wheels that came with the Doop skates. Not great wheels, but they roll well enough.

Recently I did a small test. Went to my favorite stretch of rough road and put different wheels under my left and my right skate. I compared Bont G3 84a, K2 Star Grip 85a, Bont Mayhem 85a and 87a and Bont Red Magic XFirm wheels. Was I in for a surprise, the differences where remarkable. For example I thought G3's where reasonable. But compared to these other wheels they really sucked. I binned them as soon as I came home.. What's in a wheel? It can be quite a lot.

Recently I did a small test. Went to my favorite stretch of rough road and put different wheels under my left and my right skate. I compared Bont G3 84a, K2 Star Grip 85a, Bont Mayhem 85a and 87a and Bont Red Magic XFirm wheels. Was I in for a surprise, the differences where remarkable. For example I thought G3's where reasonable. But compared to these other wheels they really sucked. I binned them as soon as I came home.. What's in a wheel? It can be quite a lot.

LOL! Funny because, Bont G3 (84a or 85a I forget which), 110mm's came with my Semi-Race skate package only I assembled everything with K2 110mm Stargrip wheels which I had stocked up on haveing come from a K2 Radical Pro. I passed the unused Bont G3 110's on to a skater replacing a Powerslide R2's package deal 3x100x90 high-low for a 4x110 frame. I had liked that the Stargrips were lightweight'ish compared to the G3's which at the time was all I had to go by.

I have never liked 3 wheels setups of any kind on rough surfaces including 3x125. I use a 5x80 frame for my 3x125 setup. On a rough surface, I would much rather have the 5x80 instead of the 3x125. Just like bjvircks, fewer wheels equals rougher ride and a bigger chance for the wheels to take wicked detours on the edges of bricks or cracks in the road. Think of it this way, 3 wheels setups are essentially teeter totters that pivot about the middle wheel. If your skates are only touching the ground on the middle wheel while going over a bump, then it doesn't take much force to make your skate spin around by pivoting about that 2nd wheel.

I experienced the center wheel pivot "wicked detours" for the first time last week while slaloming down a hill to scrub speed. Initially, I thought the short(er) 12.6" frame was great that I could slalom until the pivoting direction change occurred! Was talking about it yesterday with another 3x125 skater, saying I found the 3X setups Achilles heel. He said it happened to him at speed and was dangerously scary!

So, I have been wondering if the 3X setup would be less prone to pivot and more stable if the wheel layout would be OO--O rather than the status quo O-O-O setup? The OO--O wheel setup could also allow for a slightly lower deck height. I haven't thought out the drawbacks of OO--O wheel orientation. Any ideas?

I experienced the center wheel pivot "wicked detours" for the first time last week while slaloming down a hill to scrub speed. Initially, I thought the short(er) 12.6" frame was great that I could slalom until the pivoting direction change occurred! Was talking about it yesterday with another 3x125 skater, saying I found the 3X setups Achilles heel. He said it happened to him at speed and was dangerously scary!

So, I have been wondering if the 3X setup would be less prone to pivot and more stable if the wheel layout would be OO--O rather than the status quo O-O-O setup? The OO--O wheel setup could also allow for a slightly lower deck height. I haven't thought out the drawbacks of OO--O wheel orientation. Any ideas?

I thought about this arrangement in the past too. I would say the only downside would be the weight on each wheel will no be very even unless you intentionally sit back on your heals. The think the setup would be more stable, especially if you put weight on the balls of your feet as you would essentially be skating on two wheels (the opposite of what you want to do for best rolling resistance).

Correct.
Only I had in mind doing so in 12.4", 12.6" and 12.8" length.

Ya, this drawing was for my 5'1" wife in an attempt to make 125's work for her (which they don't). Longer frames could take advantage of the offset middle wheel for lower deck heights and possible stability improvements.